Stewart's response to a black flag for passing below the yellow line was a profane tirade that would have made the New Jersey mafia blush.

Such is the appeal of race scanners. Race teams and fans alike can listen to every word of strategy, criticism and encouragement that makes up a 500-mile day at the office.

No other sport exposes itself like racing. When was the last time a fan heard every word in a football huddle, or listened to strategy on the pitcher's mound, or was part of a halftime talk in basketball?

Radios once were used to snooker unsuspecting teams into mistakes. Now, they keep a driver, his crew and a spotter on the same page. They also have become yet another toy for race fans who just can't get enough.

''People can now get into the heads of a race driver during a race,'' said Wally Dallenbach, a part-time driver and full-time analyst for NBC Sports. ''The problem with getting into our heads is, you might not like what we're thinking.''

If a driver uses profanity or makes threats during a television or radio interview, he can be subject to sanctions by NASCAR.

The sanctioning body, which requires the use of a two-way radio during practice and races, has yet to punish anyone for their language on a scanner.

Three years ago, Tony Raines crashed while trying to qualify his pickup for a NASCAR Craftsman Truck Series race. He was unhurt, but the tantrum he threw on the radio in the moments that followed the accident prompted the sanctioning body to call in the driver, his crew chief and car owner for consultation.

What started as a necessity in racing has blossomed into big business. Nearly half the 200,000 fans will be tuned into every word said between a driver and his team at Daytona International Speedway, and thousands more will be listening on the telephone and Internet.

Racing Radio's Fan Scan is a program that allows people to buy phone cards that allow them to listen to their favorite driver during a race.

''We can take people inside the car, inside the race and expose them to the heat of the battle,'' said Chris Thornton, president of Racing Radios. ''It's the only sport where you can get the feel for what's happening. You hear the true emotion during the heat of battle.''

Since the conversation often isn't G-rated, NASCAR employs a three-second delay for radio traffic that's bought over the telephone and Internet. That gives Racing Radios time to bleep profane language, Thornton said.

Fans listening live from the grandstands hear everything.

Twenty years ago, most teams had two-way radios, although most frequencies overlapped. Teams that shared the same frequency sometimes lulled their competition into mistakes, said retired driver Benny Parsons.

''Guys used to call for a pit stop so the other teams would also make plans to stop,'' he said. ''When they slowed down to go onto pit road, you'd take off to a big lead.

''Another favorite game was to yell 'Caution, caution! Wreck in Turn 3!' When everybody slowed down, you pass them.''

The Federal Communications Commission now assigns each team their own frequency. Several radio companies compile those frequencies and sell them to their customers. And since the public can find where to listen to every team, it makes it easy for the teams to monitor each other.

Stewart said he understands the interest in hearing what goes on during the race as long as fans understand a lot of what's said comes under ex treme pressure.

''If they don't like what they hear, they can turn the scanner off,'' Stewart said. ''We don't have time to think about what to say and what's not to say. You act naturally.''